The present invention relates to an antenna apparatus for a moving body, such as an automotive vehicle, a ship and so forth. More specifically, this invention relates to an antenna apparatus for receiving on a moving body radio wave transmitted from a broadcasting satellite.
One example of the conventional antenna for a moving body is disclosed in Japanese Unexamined Patent Publication JP-A-2-159802, in which a plane antenna is divided into a plurality of antenna segments, driving signals for driving the plane antenna in azimuth direction and elevation direction, respectively, are generated on the basis of a phase angle representative of phase delay of a receiving signal of one antenna segment relative to that of another antenna segment, and controls the attitude of the antenna by driving respective motors via motor drivers on the basis of the drive signals. The antenna and the drive section are covered by a radome.
Further, a device to drive two plane antennas independently of each other with their receiving surfaces maintained in parallel to each other is also known in the art, from Japanese Unexamined Patent Publication JP-A-1-261005.
Since antenna apparatus for a moving object is generally mounted on a roof of a vehicle or the like, it is highly desirable to make it as compact as possible. Particularly, it is highly desirable to make the height of the antenna as low as possible from the viewpoint of external appearance of the whole vehicle and/or of limitation of total high of a vehicle on a road. With respect this point, the antenna apparatus disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 1-261005 is advantageous. However, this antenna apparatus requires drive mechanism for driving two antennas independently of each other. Therefore, the construction becomes complicated. Also, the weight of parts supported by an azimuth drive unit is increased to cause increasing of inertia in movement in the azimuth direction, resulting in slower response characteristics in tracing the satellite.